The relationships between behavioral dimensions of aggression, impulsivity, and concentrations of monoamine metabolites, particularly 5-HIAA, in the spinal fluid of children with disruptive behavior disorders of childhood are being examined. As part of that investigation, methodologic variables in spinal fluid studies of children are being clarified. Measurement of socio- environmental variables is being carried out to assess the relations between family environment and serotonenergic measures. Follow-up study to address the predictive validity of measurement of CSF 5-HIAA in children and adolescents is underway. To investigate the role of serotonin in the pathophysiology of ADD, 20 hyperactive boys received fenfluramine (0.6-2.0 mg/kg), dextroamphetamine or placebo in a double-blind crossover study. Fenfluramine had no behavioral effect whatsoever. However, striking biochemical changes (decreased urinary and plasma MHPG, decreased urinary NE, E and VMA). Central serotonergic effects were inferred from the increased plasma prolactin and decreased platelet serotonin. In spite of its structural similarly to amphetamine, fenfluramine has virtually noen of its therapeutic effects.